1. Field of the Invention
The present invention refers to a spark erosion machining apparatus comprising a spindle adapted to receive and clamp an electrode used for machining a workpiece into a desired shape, a displaceably mounted working table located in a certain distance below the spindle, first drive means operatively coupled to the working table to displace it with regard to the spindle within a horizontal plane in X-direction, second drive means operatively coupled to the working table to displace it with regard to the spindle within a horizontal plane in Y-direction and a tub mounted on the working table adapted to receive the dielectric liquid required for the erosion machining and to receive the workpiece to be machined.
Such spark erosion machining apparatus are more and more used in the metal machining industry; their mode of operation should be well known to any person skilled in the art and must not be explained here since it is of no further importance for the present invention. However, it must be noted in connection with the present invention that electrodes of such a spark erosion machining apparatus have to be changed frequently during the machining operation of a workpiece.
Many spark erosion machining operations of a single workpiece require that the electrode used to machine the workpiece has to be changed several times in the course of the machining operation, particularly if the control of the machining apparatus is performed more or less automatically; such a machining apparatus is in a position to perform a plurality of machining operations on a single workpiece in sequence.
2. Prior Art
In order not to disturb or interrupt this automatically running machining operation, automatically operating electrode change means have been developed which can be controlled by the same control means used for controlling the automatic operation of the machining apparatus. A typical, general example of a tool changer is disclosed, e.g. in German Laid Open Patent Application No. 28 37 719.
These problems are particularly present in connection with the electro-erosive machining of workpieces because such machining is a relatively slowly progressing machining operation. Thus, it is most desirable to automate this kind of machining operation as fully as possible.
In the prior art are known, for instance from the disclosure of German Laid Open Patent Application No. 35 33 001, electro-erosive machining apparatus incorporating an electrode change device which includes an electrode magazine in the form of an endless continuously running chain-like storage member. Further, a gripping arm is provided and operated to grasp a selected electrode and to insert it into the electro-erosive machining apparatus, and to remove the electrode from the electro-erosive machining apparatus and to put it back into the storage member, respectively. In order to ensure that the selected electrode is taken out of the magazine and that the electrode removed from the machining apparatus is put back to its proper position in the magazine, respectively, a magazine of the kind referred to above must be driven to run along a continuous path until the selected electrode or the proper storage position comes to a location where it can be reached by means of the above mentioned gripping arm.
The main disadvantages of this kind of electrode change apparatus are, on the one hand, the large space requirement and, on the other hand, the comparatively slow access speed, particularly if a large number of electrodes are in the magazine which must be ready for immediate access.
In order to avoid these disadvantages, it has been proposed, e.g. in the European Patent Application No. 0 132 599, to use a tool magazine comprising a plurality of essentially disc-shaped tool support members which are rotatable around a first axis of rotation, the tools being arranged along the periphery of the tool support members. Further, there is provided a transport arm which is pivotal around a second axis of rotation and located in a certain distance from the first axis of rotation, said transport arm being adapted to grasp the tools, to remove them from the magazine and to insert them into the machining apparatus and vice versa. Such a tool magazine requires less space and has an improved access speed.
However, there is the disadvantage that such a tool magazine is very expensive and, thus, can be reliably used only if it is necessary to have access to a comparatively great number of electrodes stored in the magazine.
In may cases, however, it is not necessary to have dozens or even hundreds of electrodes ready for immediate access, but it would be sufficient to have the possibility to change only a few electrodes automatically. Consequently, the purchasing of an automatic electrode change apparatus of the kind mentioned hereinbefore would be uneconomic.